Sulfur is not a metal. According to Wikipedia, sulfur is defined as a multivalent nonmetal. It is a nonmetal because it has the physical and chemical properties that characterize nonmetals.
Like all nonmetals, sulfur is a poor conductor of heat and electricity because its electrons are tightly held and are not free to move around. However, this physical property makes sulfur a good insulator.
Nonmetals such as sulfur have lower densities than metals, high ionization energies and high electronegativities. Sulfur easily gains electrons, does not have a metallic luster and is brittle in solid form. Sulfur oxidizes most metals and acts a reducing agent.